Left aortic arch with anomalous origin of the right subclavian artery is the most common aortic arch malformation noted on postmortem examination. The incidence of this abnormality in the general population is approximately 0.5%. The left arch has a normal course to the left and anterior to the trachea, but the right subclavian artery arises as the last branch of the arch and courses posterior to the esophagus. Most patients with anomalous right subclavian artery are asymptomatic, and the abnormality is discovered incidentally at esophagography or at catheterization. Often, an anomalous right subclavian artery is seen in patients with tetralogy of Fallot and left aortic arch and, therefore, has a significant bearing on which systemic-to-pulmonary artery shunt is chosen for palliation of cyanosis. In addition, an anomalous right subclavian artery may be present in patients with coarctation of the aorta, and it often arises distal to the site of coarctation. In these patients, blood pressure in the right arm and legs does not reflect the coarctation gradient. It is necessary, then, to determine blood pressure in both arms and in the legs during the examination of patients with suspected coarctation.

Although most patients with an anomalous right subclavian artery are asymptomatic, some older children and adults may experience dysphagia. Routine chest radiography does not demonstrate this anomaly, but barium esophagography is diagnostic. The oblique course of the anomalous vessel posterior to the esophagus in the anteroposterior projection and the posterior indentation of the esophagus in the lateral or left anterior oblique projection usually are diagnostic (Fig. 280.1). The diagnosis of an anomalous right subclavian artery may be made using two-dimensional echocardiography when the first branch of the aorta is to the right, but the normal bifurcation into a right carotid artery and right subclavian artery cannot be demonstrated. An anomalous right subclavian artery may be noted incidentally when aortography is performed in patients with congenital heart disease.

If symptoms of a vascular ring (e.g., stridor, wheezing, cough) are present in a patient with an anomalous right subclavian artery, an alternative diagnosis, such as laryngomalacia or tracheomalacia, should be considered. Rarely, an anomalous right subclavian artery in association with a left aortic arch, retroesophageal descending aorta, and right ductus arteriosus or ligamentum produces a symptomatic vascular ring. The retroesophageal descending aorta in these patients results in a large, rounded, posterior indentation on barium esophagogram, which usually is distinguished readily from the more shallow indentation produced by an anomalous right subclavian artery without a retroesophageal descending aorta. The diagnosis should be confirmed by magnetic resonance imaging (MRI).

The double aortic arch is the most common clinically recognized form of vascular ring. The ascending aorta divides anterior to the trachea into left and right arches, which then pass on either side of the trachea. Usually, the right arch is larger than is the left, and it passes posterior to the esophagus to join the descending aorta to the left of the midline. Uncommonly, the left arch is atretic. A complete vascular ring is formed by the arches on each side of the trachea and esophagus, with the ascending aorta anterior and the retroesophageal arch or descending aorta posterior. Usually, the ductus arteriosus is left-sided and is not an essential component of the vascular ring, but the length of the ductus arteriosus or ligamentum may affect significantly the severity of symptoms. Usually, associated congenital heart disease is not present, but it may occur in as many as 22% of patients. Cyanotic congenital heart disease, including tetralogy of Fallot and transposition of the great arteries, predominates.

Usually, patients with a double aortic arch are severely symptomatic in infancy, with stridor, dyspnea, cough, and recurrent respiratory infections. Infants feed poorly because of severe respiratory distress and may prefer to assume an opisthotonic posture. Life-threatening episodes of apnea with cyanosis may occur. The diagnosis of a double aortic arch, like almost all vascular rings, often is suggested by the presence of a right aortic arch on routine chest radiography. In patients with a double aortic arch, both arches sometimes are seen, and evidence of hyperinflation of either or both lungs caused by obstruction of the lower trachea and mainstem bronchi may be present.

Barium esophagography often demonstrates bilateral indentations of the esophagus in the anteroposterior projection (Fig. 280.2) but may show only a prominent right-sided indentation. When two indentations are seen, usually the right arch produces the larger and more superior indentation. In the lateral or left anterior oblique projection, a large posterior indentation is seen and represents the retroesophageal component of the arch. Also present is an anterior and more inferior indentation of the arch produced by posterior deviation of the trachea. Although surgery may be performed without additional imaging studies, confirmation of the diagnosis can be obtained by MRI, echocardiography, or angiography. MRI provides sufficient anatomic detail to perform surgery and may even demonstrate tracheal compression (Fig. 280.3).

Usually, stridor and respiratory distress are severe, and affected infants will die without early surgical intervention. The mortality rate from surgery is low, and usually eventual

long-term relief of symptoms is achieved. However, short-term postoperative tracheal obstruction is the rule, and some infants require prolonged intubation and aggressive attention to pulmonary toilet in the early postoperative period. Stridor may persist to some degree for months after surgery.